Those fires sound interesting what history is known?.

Well, looks like nothing much remains. I guess those New Year Fire Festivals at various places are reinventions of something or other.

As to The Celts of the celts the most recent academic book on who was who, who is who and where did we come from is "The Origins of the British" by Stephen Oppenheimer. An impressive book that covers language, genes and so on. He dismisses the idea of a Celtic Homeland in Central Europe and places the origins of the Celts in Spain / South West France. He also argues from extensive evidence that much of England was not Celt.

Ok I am only half way through a difficult read but it largely supports the Spain, France, Cornwall, Wales, Ireland hypothesis.